Frost gravure print master



May 20, 1969 R. w. GUNDLACH ET AL 3,445,226

- FROST GRAVURE PRINT MASTER Filed May 24. 1965 mmm@ Illll 7) W9 m I NVENTORS ROBERT W. GUNDLACH LLOYD F. AN

BY I

United States Patent O 3,445,226 FROST GRAVURE PRINT MASTER Robert W. Gundlach, Victor, and Lloyd F. Bean, Rochester, N.Y., assignors to Xerox Corporation, Rochester, NX., a corporation of New York Filed May 24, 1965, Ser. No. 458,282 Int. Cl. G03 13/14, 13/12 U.S. Cl. 961.1 14 Claims ABSTRACT OF THE DISCLOSURE The present invention relates generally to printing masters and more particularly to those printing masters which may be conveniently prepared by techniques encompassed in the art of xerography. The invention includes both a novel printing master and the methods utilized in its preparation.

In the copending application of Robert W. Gundlach entitled Electrostatic Frosting, Ser. No. 193,277, tiled May 8, 1962 and :assigned to the same assignee as the present invention, techniques are disclosed for the first time which are capable of producing unique continuous tone deformation images upon the surfaces of suitably chosen thermoplastic materials. These frosted images as they are referred to in the referenced application, can, among other things, be directly utilized in connection with printing processes resembling gravure. These applications of frosted images are fully elucidated at pages 331?c of the referenced specification. On page 34, for example, one such gravure type technique is described wherein an ink is lightly wiped over such a frosted image and allowed to brieiiy dry. The image is then moisteued and wiped so that the ink is primarily removed in background areas, but retained in the finely convoluted frosted areas. The resulting inked image is thereupon found to display capabilities of printing in high resolution, continuous tone.

While frosted thermoplastic surfaces have accordingly been `found to make generally effective gravure type printing masters, yet it will be appreciated by those skilled in the art that several types of defects can be introduced into such masters by the very techniques by which they are prepared. In particular, it Will be apparent that even though only a limited portion of the image bearing thermoplastic surface will contain the frosted ink-retaining areas, yet all portions of the surface are involved in the prior thermoplastic deformation process at the time of image formation. Therefore, background areas as Well as frosted information bearing areas have a history ot subjection to heat softening. This can, and sometimes does, result in warping of the background surface and may induce as well minor surface imperfections in the background due to trapped dirt particles or to heat expansion of minute inclusions previously present within the thermoplastic material. Such background imperfections appear upon subsequent use of the surface for printing.

Furthermore, since in such prior art the frosted image is initially formed upon an entire uniformly constituted thermoplastic surface, it is not readily possible to optimize conditions -for maximum ease and degree of frosting in one part of this uniform surface to the neglect of what may happen at another point on the same surface. This 3,445,226 Patented May 20, 1969 is to say that one cannot specifically optimize conditions for frosting at the information-bearing portions of such a surface (by e.g., very high charging and/or heating) without expecting that distortion of the thermoplastic will ultimately begin to occur at the background (non-information bearing) portions of the surface as Well.

It is accordingly, one object of the present invention to provide a method for preparing a printing master having frosted printing portions thereon, wherein optimization of the conditions for creating maximum frost density at information-bearing portions of the master can be achieved without detrirnentally affecting the non-information bearing portions of the master.

It is another object of the present invention to provide a method whereby frosted image configurations suitable for use as printing elements, may be formed upon unwarped, smooth, and dimensionally stable backgrounds.

It is a further object of the present invention to provide a method whereby frosted image-bearing printing masters may be created with such a high degree of versatility that structures previously unattainable become feasible.

It is yet another object of the present invention to provide new and highly effective printing masters that may be prepared by the rapid and expeditious methods of xerography and electrostatic frosting.

Now in accordance with the present invention, it has been found that excellent quality printing masters may be prepared by direct deposition of a frostable material, as for example, a xerographic toner comprised of frostable resin, in image configuration upon a relatively inert, relatively heat stable substrate. The frostable material is normally deposited upon the chosen substrate in a particulate form. Thereafter, such frostable material together with the underlying substrate is, in a typical embodiment of the invention, subjected to a combination of electrical charging and heating to Whatever degree may be necessary to .achieve the desired frosting of the previously `deposited material. Since the underlying substrate will have a softening and melting point much higher than the configurated frostable material, it follows that the high degrees of heating and/or charging that may be necessary to assure optimum frosting in the configurated image will not in any way adversely affect the underlying substrate. The heating `of the deposited material acts not only in conjunction with charging to cause frosting, but acts of itself to cause as well, fusing of the deposited material to the substrate.

The invention as illustrated by way of example in the accompanying drawings, in which:

FIGURE 1 diagrammatically illustrates the manner in which a printing master may be prepared in accordance with the present invention; and,

FIGURE 2 diagrammatically illustrates the manner in which a master prepared pursuant to the present invention may `be used for printing upon an ink receptive surface.

In FIGURE 1A, a conventional xerographic plate 1 which may, by way of example, comprise a layer of vitreous selenium 3 upon a conductive `substrate 4, is shown bearing a latent electrostatic image 5 upon the photoconductive surface. Such a latent image is formed by the usual methods of xerography; that is, by charging the plate in darkness, and thereafter exposing to a pattern of light in the form ofthe image one desired to reproduce. In FIGURE 1B, the latent image is shown developed by the particulate composition 7.

It will, 'of course, be recognized by those skilled in the art that so far no more than the usual steps of Xerography have been performed, and in the usual course of reproducing an image upon a sheet of paper or the like, the material comprising composition 7 would be chosen to have among other characteristics high visibility upon subsequent transfer of the image to the copy sheet. In the present invention, however, the choice of composition 7 is dictated principally by the frosting characteristics of the material chosen. As has been previously indicated, a full discussion of frost may be found in the Gunther and Gundlach application referenced, but by Way of summary, it may be stated that thermoplastic materials are known which, when subjected to appropriate combinations of electric charge and softening will develop surface deformations comprising generally a finely dispersed pattern of minute alternating depressions and elevations throughout all areas of the thermoplastic surface at which a sufficient electric field is present. Thus, for purposes of the present specification, such materials will be referred to as frostable materials and in consequence of the common terminology used in the practice of xerography, composition 7 may hereinafter be referred to as a frostable toner.

By way of example, composition 7 may comprise a particulate composition of Staybelite 5 or Staybelite 10, both of which materials are rosin esters available under the trade names indicated from the Hercules Powder Company. Composition 7 may also suitably comprise finely ground Piccotex, a copolymer made from alpha-methyl styrene and vinyl toluene and available from the Pennsylvania Industrial Chemicals Company. Finely ground Piccolastic A-75, which is essentially a polystyrene composition available from the Pennsylvania Industrial Chemicals Company, is yet a further example of a material well suited for composition 7. A more extensive listing of other materials suitable for the present purpose may be found at page 31 of the referenced Gunther and Gundlach specitication. However, the list there enumerated is intended by no means to be limiting here, since as will be subsequently pointed out, the present invention by its nature will lend itself to a vast number of materials.

In FIGURE 1C, the developed particulate image is shown being transferred to substrate 9. Where, as is illustrated, substrate 9 comprises a dielectric material, this may be readily brought about by positioning the sheet of dielectric against the developed image and covering the rear side of the sheet with a charge distribution supplied from corotron generators 8. For purposes of illustrating the present invention, substrate 9 may be considered to be a sheet of a relatively high melting point inert plastic such as, for example, the sheet polyethylene terephthalate commonly available under the trade name Mylar. However, it will `be appreciated that substr-ate 9 may equally well be chosen from any of a limitless number of materials. Since substrate 9 merely forms the support vehicle for the image that is subsequently used for printing purposes, the -only limitation placed upon it is that it have a melting point higher than the frostable toner it bears, that it be relatively dimensionally stable, and that it be relatively smooth and impervious to the ink that will subsequently be coated upon it in its use as a master. Thus, substrate 9 need not be chosen as a plastic-like material at all, but may be a dense, refractory material such as glass, or even metal. In the latter case, the conductive nature of the substrate introduces some special peculiarities into the present process. By this is meant, for example, that transfer of a developed image from a Xerographic plate must be brought about by the use of, for example, an intermediary transfer sheet or by the induction transfer method described in U.S. Patent 3,004,860 by Gundlach. In addition, charge focusing effects introduced by the low potential background of such a metal substrate require the use of higher corona charging currents in order to deposit sufficient charge on the insulating image to cause high density frosting.

It will be appreciated by those skilled in the art that if the support member which has been referred to as substrate 9 possesses photoconductive properties, the steps shown in FIGURES 1A, B, and C can be dispensed with as the coniigurated toner image could then be formed directly upon the substrate. An example of a substrate satisfying these requirements is zinc oxide paper. The combination of zinc oxide coated upon a metallic plate is a further example. Numerous examples could also `be cited using higher melting point organic photoconductors overcoated on metal plates or paper or the like.

In FIGURE 1D, frosting of the developed image 7 upon the substrate 9 has been brought about by subjecting the combination to the simultaneous action of heat from heat source 11 and charging from the traversing corotron generator 19. Where, as is illustrated, substrate 9 comprises a dielectric material, a conductive supporting plate 15 is positioned beneath the substrate 9 so that the high voltage source 13 may conveniently be connected to plate 15 and to the corotron generator 19, and a field established between the two, thereby facilitating the flow 0f charge to the image-bearing surface of the dielectric.

Of major importance to the present invention is the fact that the operation depicted in FIGURE 1D need not be performed with any high degree of exactitude. The heating and charging of the substrate 9 bearing the configurated frostable toner, is, in the embodiment illustrated, carried out simultaneously. The degree and intensity of heating and of charging is not governed by any rigid parameters, but may for all practical purposes, be increased until a point is reached at which the desired frosting of the conligurated toner occurs. Perhaps the limits of heating and charging will only be `reached when dielectric breakdown and/or melting of the substrate 9 begins to occur. In practice, however, as the principal object of the heating is to soften the conligurated toner and simultaneously fuse it to the substrate, it is obvious that the upper limit of heating will not normally be approached.

In any event, it will be clear to those skilled in the art that the overall approach depicted in FIGURE 1D to achieve frosting is quite at variance with the much more delicate and precise operations utilized in the prior art. The reason for this of course, is that in such prior art, a latent electrostatic image was always present upon the surface of the thermoplastic upon which a frosted image was to Ibe formed. Consequently, charge could not be poured upon this latent image indiscriminantly, lest the image be altered before any development had taken place. Neither could heating or other softening means be used indiscriminately in such prior art, for once again, excessive softening could cause dissipation of the latent charge image. But in the present invention, these several restraining factors are of no significance, since the latent image has been developed prior to the time the frosting process is invoked. Therefore, a massive attack may be safely made upon the frostable material constituting the image configuration, and one may safely concentrate upon creating ideal conditions for deformation of the surface of such frostable material without concern in any way for possible adverse side effects at background areas on the substrate.

While in FIGURE 1D the frosting of the developed image has been brought about by the conjunctive action of heating and charging, it will be clear that the principal function of the heating portion of this combination is to soften the frostable material so that the desired deformation may take place under the influence of the electric fields induced by the applied charges. As is well known in the prior art, and as if, for example, fully discussed in the Gunther and Gundlach application previously alluded to, such softening action may be brought about by solvent vapors as well as by heating. Thus, for example, it is well known that with the thermoplastic compositions Staybelite 5, Staybelite 10 or Piccotcx, the necessary softening action may be brought about by exposure to the vapors of the solvent trichloroethene.

Preparation of the printing masters in the foregoing paragraphs has been considered principally from the viewpoint of a situation where one desires to reproduce a relatively complicated graphic pattern, such as for example, a

page of printed material. Where the material to be reproduced is thus complex, the use of the illustrated Xerographic techniques to provide at some point in the process a developable latent electrostatic image is highly desirable. It will be apparent, however, that it is quite possible to prepare printing masters corresponding to the present invention by depositing frostable toner in image configuration upon a chosen substrate without the use of any latent electrostatic image whatsoever. Thus, the frostable toner could be deposited directly upon the substrate by dusting through a stencil; or, a pattern could be laid down by free-hand deposition from any convenient dispenser, or toner development of a very faint liquid image, such as is deposited by vapor thermography methods could be used. Thereafter, the frostable toner would be treated as in FIGURE 1D to render the surface of the toner capable of retaining ink.

FIGURE 2 diagrammatically illustrates the manner in which a typical printing master prepared pursuant to the processes elucidated in the foregoing paragraphs, may be used for printing upon an ink receptive surface. As shown in FIGURE 2A, the master comprises the substrate 20 which now bears fused to its surface the image configurated frosted toner 22. For purposes of illustration only, the substrate may again be considered to be a relatively thin sheet of Mylar. Since in such a case the master will be highly flexible, it will be necessary for the present purposes to provide a support means such as base 21. The master is shown being inked from an ink source 23, which exudes quantities of liquid ink as it traverses the master surface from right to left in the sense of the diagram.

As illustrated in FIGURE 2B, a rubber bladed squeegee 27 or the like is then passed across the surface of the master. As the rubber blade passes from right to left in the sense of the diagram, the intimate contact established between blade and master surface effectively removes ink from all of the smooth background areas of the subbstrate; but within the vast multiude of minute surface interstices which now comprise the frosted surface of the configurated tone image, ink remains.

In FIGURE 2C an ink receptive surface 31 is brought into contact with the inked printing master. Ink now readily ows from the multifarious convolutions of the frosted surface to the ink-receptive surface to be printed. As shown in the diagram a roller 29 may be used to assist in maintaining good contact between'the surface to be printed and the master. While for purposes of the present illustration 31 may be considered to be a sheet of paper, it will be clear that any ink receptive surface may be printed in essentially the same manner.

In FIGURE 2D, the printed surface is shown being removed from contact with the printing master. The same process may now be repeated over an indefinite number of cycles.

While FIGURE 2 has illustrated one specific embodiment in which printing masters prepared pursuant to the present invention may be employed, it will be obvious that myriad configurations are possible utilizing similarly prepared masters. So, for example, the same master shown in FIGURE 2 as comprising the flexible substrate Mylar and bearing the frosted toner configuration, can be mounted upon the surface of a rotating cylinder, whereby multiple copies may be readily produced by the identical scheme shown in FIGURE 2. Moreover, since as previously indicated, the frosted toner may by the present invention be deposited directly upon a metallic or other rigid support surface, it follows that the frosted toner configuration might as well be deposited directly upon the face of the rotating cylinder just alluded to. Thereafter, the inking, squeegeeing, and printing steps would essentially conform to the scheme shown in FIG- URE 2.

While the invention has been illustrated and described with reference to particular embodiments thereof it will be clear that numerous changes and various modifications thereof may be made by those skilled in the art without yet departing from the spirit and scope of the invention.

What is claimed is:

1. A method for preparing a printing master comprismg:

(a) depositing a frostable toner in image configuration upon a supporting substrate, said substrate having a higher softening point than said frostable toner; and

(b) simultaneously charging and softening said toner upon said substrate to fuse said toner to said substrate and to frost said toner without frosting said substrate.

2. A method for preparing a printing master from a graphic representation comprising in sequence the steps of:

(a) exposing a charged Xerographic plate to the light pattern corersponding to said graphic representation, thereby forming a latent electrostatic image of said representation;

(b) developing said latent electrostatic image with a frostable particulate toner;

(c) transferring said toner in image configuration to the surface of a supporting substrate having a higher softening point than said frostable toner; and

(d) simultaneously charging and softening said toner upon said surface of said substrate to fuse said toner to said substrate and to frost said toner without frosting said substrate.

3. A method for reproducing a graphic representation comprising in sequence the steps of (a) exposing a charged Xerographic plate to the light pattern corresponding to said graphic representation thereby forming a latent electrostatic image of said representation;

(b) developing said latent electrostatic image by application of a frostable particulate composition thereto;

(c) transferring said composition in the configuration of said image to the surface of a supporting substrate, said substrate having a higher softening point than said frostable composition;

(d) simultaneously charging and softening said composition upon said surface of said substrate to fuse said composition to said substrate and to frost said toner without frosting said substrate;

(e) applying ink to said frosted composition in said image configuration upon said substrate; and

(f) contacting said composition in image configuration upon said substrate with an ink receptive surface upon which said graphic representation is to be reproduced.

4. A method for preparing a printing master comprisz(la) depositing a frostable particulate composition in image configuration upon a supporting substrate, said substrate having a higher softening point than said frostable composition;

(b) fusing said composition to said substrate and frosting the surface of said fused composition without frosting said substrate.

5. A method for preparing a printing master compris- (a) depositing a frostable toner in image configuration upon a supporting substrate;

(b) simultaneously charging and softening said toner upon said substrate to fuse said toner to said substrate and to frost said toner without frosting said substrate.

6. A method for preparing a printing master for a graphic representation comprising in sequence the steps of (a) depositing a frostable particulate composition in image configuration upon a smooth, ink-impervious substrate, said substrate having a softening point higher than the softening point of said frostable composition;

(b) exposing said substrate and said composition to continual charging, .and simultaneously heating said composition and said substrate to a temperature above the softening point of said composition, but below the softening point of said substrate, whereby said composition is fused to said substrate and is made to frost;

(c) permitting said substrate and said composition to cool.

7. A method for preparing a printing master comprising:

(a) depositing a frostable composition in imagewise conguration upon a supporting substrate, said substrate having a higher softening point than said frostable composition; and

(b) frosting said composition without frosting said substrate.

8. A method according to claim 7 wherein said frosting includes the steps of softening said composition and supplying electric charge to the surface of said composition.

9. A method according to claim 8 wherein said softening is brought about by application 0f heat.

10. A method according to claim 8 wherein said softening is brought about by exposure of said composition to the vapors of a solvent for said composition.

11. A method according to claim 8 wherein said supplying of electric charge and said softening are brought about simultaneously.

12. A method for preparing a printing master comprising:

(a) depositing a thermoplastically deformable com- 8 position in image configuration upon a supporting substrate, said substrate having a higher softening point than said thermoplastically deformable composition; and

(b) charging and softening said composition upon said substrate to fuse said composition to said substrate and to deform said composition without deforming said substrate.

13. A printing master comprising a smooth surfaced supporting substrate, a surface of said substrate being non-deformed and bearing in image configuration a thermoplastically deformed composition raised from and supported by said surface, said composition being fused to said surface at points of mutual contact.

14. The printing master of claim 13 wherein said substrate is ink-impervious.

References Cited UNITED STATES PATENTS 2,637,651 5/1953 Copley 961.4 X 2,917,460 12/1959 Solar 252-621 3,093,039 6/ 1963 Rheinfrank 96-1.4 X 3,196,011 7/1965 Gunther et al. 96-1.1 3,271,146 9/ 1966 Robinson 96-1.4 3,307,941 3/ 1967 Gundlach 961.1

I. TRAVIS BROWN, Primary Examiner.

C. E. VAN HORN, Assistant Examiner.

U.S. Cl. X.R.

96-1, 1.4; lOl-368, 395, 401.1; 117--17.5; 250-65 

